1. Field of the Invention
Methods and apparatuses consistent with the present invention relate generally to an image signal processing, and more particularly, to an image signal processing capable of carrying out a dithering without using a frame buffer.
2. Description of the Related Art
An image signal processing apparatus, such as a plasma display panel (PDP), which processes image signals to display on a screen, receives the image signals including broadcasting signals from various image outputting media, such as a video cassette recorder (VCR) and a digital video disk (DVD) player, to reproduce on the screen. Once image signals are received, the image signal processing apparatus reproduces processing image signals of red (R), green (G) and blue (B), and to enhance luminance characteristics, carries out reverse gamma compensation to the image signals of red (R), green (G) and blue (B).
However, when the reverse gamma compensation is carried out, noise occurs in low gradation areas and thus image quality is deteriorated. To prevent such a deterioration of the image quality, a dithering is carried out. A conventional dithering method is described with reference to FIG. 1 as follows.
FIG. 1 is a schematic block diagram illustrating a conventional image signal processing apparatus.
Referring to FIG. 1, the conventional image signal processing apparatus includes a random producing unit 10, a frame buffer 30, a dithering processing unit 50, and an adding unit 70.
The random producing unit 10 produces seed values for respective frames f of input image signals. At this time, the random producing unit 10 produces a seed value for every M×N position of each of the frames f by using position (x, y) information of pixels. Here, the seed value is a value for determining a mask matrix, which is used in carrying out a dithering at the dithering processing unit 50 to be described later.
The seed values produced from the random producing unit 10 are stored in the frame buffer 30 for one period, and the dithering processing unit 50 determines mask matrixes by using the seed values stored in the frame buffer 30 and then carries out the dithering process by using the mask matrixes. A period includes more than one frame, and whenever the period is changed, new seed values are produced from the random producing unit 10 and are stored in the frame buffer 30.
The adding unit 70 adds the dithered image signals to the input image signals r, g and b and outputs image signals r′, g′, and b′ with improved image quality.
Here, to carry out a spatial dithering, the seed values produced with respect to M×N positions of each of the frames are used, and to carry out a temporal dithering, the seed values stored in the frame buffer 30 for the one period are used. However, it is expensive to implement in hardware or to physically embody the frame buffer 30 in the image signal processing apparatus. On the other hand, if the image signal processing apparatus is not equipped with the frame buffer 30, it is impossible to carry out the temporal dithering and thus to realize a high-definition image.